Ducks killed on a poultry farm in North Jeolla Province in the weekend to prevent bird flu from spreading.(Yonhap News)

South Korea on Monday confirmed the presence of avian influenza (AI) in a group of migratory birds found dead last week, suggesting a possible cause for the recent infection of birds at poultry farms and raising concern that the infection may spread further.

Tests were conducted after some 100 migratory birds were found dead at a reservoir in North Jeolla Province in the country's southwest over the weekend, following an outbreak of AI at several duck farms. Three bird flu cases, including two confirmed cases, have been reported at poultry farms in Gochang and Buan, all in the vicinity of the reservoir.

"Though we have yet to have a definite diagnosis, it (thevirus) is highly expected to be of a highly pathogenic strain, which might explain the source of AI virus that affected the duck farms in Gochang and Buan," the Ministry of Agriculture, Food and Rural Affairs said in a press release.

The virus found in the migratory birds has been confirmed to be the H5N8 strain, the same type that affected the birds at the duck farms located some 300 kilometers south of Seoul.

Whether the virus found in the migratory birds is highly pathogenic will be determined later in the day. (Yonhap)